1. Preheat your oven to 350°F. Grease a 9×13-inch baking dish and set aside.
2. Bring a large pot of salted water to a boil. Cook the macaroni according to package instructions until al dente. Drain and set aside.
3. In a large saucepan, melt the butter over medium heat. Stir in the flour and cook for about 1 minute until it forms a paste.
4. Gradually whisk in the milk and cream, stirring constantly until the mixture thickens, about 5 minutes. It should coat the back of a spoon.
5. Remove the saucepan from heat and stir in the cheddar, mozzarella, and Parmesan until melted and smooth.
6. Season with garlic powder, onion powder, smoked paprika, salt, and pepper.
7. In a skillet, heat olive oil over medium-high heat. Sauté the shrimp until just pink and opaque, about 3-4 minutes. Set aside.
8. Combine the cooked macaroni, cheese sauce, shrimp, and crab meat in a large bowl. Mix well to ensure everything is evenly coated.
9. Pour the mixture into the prepared baking dish. If using, sprinkle breadcrumbs over the top.
10. Bake for 20-25 minutes until golden and bubbly. Garnish with chopped parsley before serving.

Remember, cooking times can vary depending on your oven, so keep an eye on that golden crust!